1. Field of the Invention
The present invention relates to a supporting mechanism for use with a pinch roller unit which causes a magnetic tape, used in a magnetic recording/reproducing apparatus or the like, to be in pressure contact with a capstan shaft.
2. Description of Related Art
FIG. 2 is a top view of a magnetic recording/reproducing apparatus. FIG. 6 is a cross-sectional view of a supporting mechanism for a conventional pinch roller unit.
Referring to FIGS. 2 and 6, a cassette 60 houses the tape 6 therein with a magnetic tape 6 wound on reels. A guide roller 12 draws the magnetic tape 6 out of the cassette 60 and wraps the magnetic tape 6 round a rotating drum 10. The drum 10 is provided with magnetic heads which record the video signal and audio signal on the magnetic tap or reproduce the signals from the tape.
A pinch roller unit 20 presses the magnetic tape 6 against the capstan shaft 16 so that the magnetic tape 6 travels at a constant speed. A tape guide mechanism 9 guides the travel of a magnetic tape 6. The magnetic tape 6 runs between the capstan shaft 16 and the pinch roller 20 and passes an A/C head (audio control head) 15 which reads the audio signal and control signals recorded on the magnetic tape 6.
Then, the magnetic tape 6 passes an erase head 13 and is further guided by a post pin 14 before being taken up into the cassette 60. The erase head 13 erases the signals recorded on the magnetic tape 6. The post pin 14 defines an angle at which the magnetic tape 6 is wrapped round a back tension mechanism 11. The back tension mechanism 11 controls a tension applied to the magnetic tape 6. All of the aforementioned structural elements are carried on a chassis 1.
FIG. 6 shows one 20 of known pinch roller assembly 20 of the aforementioned type. Referring to FIG. 6, the pinch roller assembly 20 includes a pinch roller 21, fixing shaft 25 on which the pinch roller 21 is rotatably mounted, and a pivot arm 26 that holds the fixing shaft 25 so that the fixing shaft vertically rises from pivotal arm 26. The pinch roller 21 includes a rubber roller 21a, core metal shaft 21b, ball bearing 22, and bushing 21c. The rubber roller 21a presses the magnetic tape 6 against the capstan shaft 16, thereby allowing the magnetic tape to travel at a constant speed. The core metal shaft 21b is a hollow cylinder and has a stepped portion. The rubber roller 21a fits over the core metal shaft 21b for secure engagement. The ball bearing 22 inserted into the core metal shaft 21b and abuts the stepped portion. The bushing 21c serves as a stopper that prevents pull-out of the ball bearing 22. A cap 23 is mounted on an upper portion of the support shaft 25b to restrict the movement of the pinch roller 21 in the thrust direction.
The fixing shaft 25 is formed of, for example, stainless steel (SUS) in one-piece construction and includes a flange shaft 25a and a supporting shaft 25b. The flange shaft 25a supports the pinch roller 21 at a predetermined height with respect to the magnetic tape 6. The supporting shaft 25b supports the ball bearing 22 thereon.
The one-piece construction of the flange shaft 25a and supporting shaft 25b has a disadvantage that fine adjustment of the marginal movement in the thrust direction and height of the pinch roller 21 cannot be made with respect to the magnetic tape 6.
The shape of the boundary between the flange shaft 25a and support shaft 25b is complex and is difficult to be machined. Moreover, the support shaft 25b is difficult to machine for sufficient smoothness of its cylindrical surface.